In this paper, we study the perturbation of spectrums of
2
×
2
2 \times 2
operator matrices such as
M
C
=
[
A
a
m
p
;
C
0
a
m
p
;
B
]
{M_C} = \left [ {\begin {array}{*{20}{c}} A & C \\ 0 & B \\ \end {array} } \right ]
on the Hilbert space
H
⊕
K
H \oplus K
. For given A and B, we prove that
\[
⋂
C
∈
B
(
K
,
H
)
σ
(
M
C
)
=
σ
π
(
A
)
∪
σ
δ
(
B
)
∪
{
λ
∈
C
:
n
(
B
−
λ
)
≠
d
(
A
−
λ
)
}
,
\bigcap \limits _{C \in B(K,H)} {\sigma ({M_C}) = {\sigma _\pi }(A) \cup {\sigma _\delta }(B) \cup \{ \lambda \in C:n(B - \lambda ) \ne d(A - } \lambda )\} ,
\]
where
σ
(
T
)
,
σ
π
(
T
)
,
σ
δ
(
T
)
,
n
(
T
)
\sigma (T),{\sigma _\pi }(T),{\sigma _\delta }(T),n(T)
, and
d
(
T
)
d(T)
denote the spectrum of T, approximation point spectrum, defect spectrum, nullity, and deficiency, respectively. Some related results are obtained.